class Counter {
    private int count = 0;

    synchronized public void add() {
        count++;
    }

    public static void func() {
        synchronized (Counter.class) {
            // ....
        }
    }


    public int get() {
        return count;
    }
}

public class Demo20 {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        Counter counter2 = new Counter();
        // Object locker = new Object();

        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                // counter.add();
                counter.func();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                // counter2.add();
                counter2.func();
            }
        });
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("count = " + counter.get());
    }
}